So I've finally upgraded to GIMP 2.8, finding that .abr was native. I've downloaded thousands of brushes, only a hundred work, MAYBE. I'm confused because even the brushes that are not in .abr form do not work. Also, sometimes if I try to fix the brushes by uninstalling and reinstalling there will be random ones that work and then old ones disappear?

ABR isn't native. It's Photoshop's file format, and not all revisions of that file format are supported.

Also, I don't understand this part: "even the brushes that are not in .abr form do not work". That makes no sense :) If you download some arbitrary file, why would it work? If those were GIMP's GBR brushes, that would be an entirely different thing, of course, but you didn't provide a clue :)

So, I'm afraid, you will need to elaborate a bit on the files you are talking about.

Alexandre

oh I'm sorry, I read that wrong somewhere. Okay, NOT native. I'm not sure what format they are in but it's the brush that you can see, I believe it is jpg or png. Typically the brushes I use that I'm not sure are in .abr format are just a white page in the brushes. However, the ones that worked on 2.6 for me, are the brushes that you can see the image. I've attached a link to show you what I meant, I hope it helps.